You want to change the folder the game saves to? Like how Halo 2 saves to 4d530064 (Is that right? It's been like 5 years)? I think that's in the xbe and you'd want to use an xbe editing tool to change it. I'm pretty sure this can do it. Should be under XBE Settings > General.

tbh though it's been so long I don't remember how all this stuff works.